A biochemical study of the biological clock of the fungus, Neurospora crassa, is proposed. We will employ a particular mutant strain, bd, since it expresses this clock at the morphological level by a rhythmic pattern of spore formation (conidiation). This rhythm is circadian in that its period is 22 hours, is temperature-compensated and its phase can be altered by flashes of light. The key idea in this proposal is that unsaturated fatty acids play a significant role in the mechanism of the biological clock. This proposition is derived from three lines of evidence: a) supplementation by unsaturated fatty acids, such as linoleic (18:2) or linolenic (18:3), increases the period of the rhythm in a fatty acid requiring strain (bd cel) from 21 hours to 40 hours and 33 hours respectively; b) there is an oscillation in the levels of 18:2 and 18:3 in the phospholipids of the bd and wild-type cultures; c) supplementation of bd cel cultures with 18:2 leads to a loss of the temperature compensation mechanism. We propose to focus our studies as to how, at the chemical level, 18:2 supplementation alters these 2 key features of the clock, i.e., periodicity and temperature compensation. C14 labelled 18:2 in the media will be employed and the amount and location of the label in the cellular lipids will be determined in the bd cell (40 hours) and bd (21 hours) cultures. Possible conversion of the label to other fatty acids will be monitored. Follow-up studies on the effects of temperature on the metabolism of the exogenous C14 18:2 in bd cel and bd cultures are also proposed. Other studies of fatty acid metabolism involve the use of a mutant strain blocked in unsaturated fatty acid synthesis (ufa), and further analysis of the 18:2 and 18:3 oscillations in the bd strain at the level of the individual phospholipids. The studies in this proposal are viewed as studies of a basic cellular regulatory mechanism, widespread in eucaryotic cells, and yet completely undescribed in biochemical terms.